<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /*body总有一个默认的外边距margin:0  常见操作*/
        /*h1,ul,li,a,body{
            margin:0;
            padding: 0;
            text-decoration: none;
        */
        /* border:粗细 样式  颜色*/
        ul,h1,li,a,body{
            margin:0;
            padding: 0;
            text-decoration: none;
        }

        #box{
            width: 300px;
            border:1px solid red ;

        }
        h2{
            font-size: 16px;
            background: cornflowerblue;
            line-height:30px;
            margin: 0;
            color: white;
        }
        form{
            background: coral;
        }
        div:nth-of-type(1)>input{
            border: 3px solid blue;
        }
        div:nth-of-type(2) input{
            border: 3px dashed black;
        }
        div:nth-of-type(3) input{
            border: 3px dashed purple;
        }
    </style>
</head>

<body>
<div id="box">
    <h2>会员登录</h2>
    <form action="#">
        <div>
            <span>用户名</span>
            <input type="text">
        </div>
        <div>
            <span>密码</span>
            <input type="text">
        </div>
        <div>
            <span>邮箱</span>
            <input type="text">
        </div>
    </form>
</div>
</body>
</html>